The objective of the proposed research is to describe the cholesterol esterification systems in rat intestine, mucosal cholesterol esterase and acyl CoA:cholesterol acyltransferase (ACAT) with respect to the following: Cholesterol esterase: a. To degine the mechanism of entry of pancreatic cholesterol esterase into mucosal cells were it functions as mucosal cholesterol esterase. b. To purify mucosal cholesterol esterase by affinity chromatography and determine directly its properties relative to pancreatic cholesterol esterase. c. To determine the physiological substrate(s), i.e., luminal and/or biosynthetized cholesterol, for cholesterol esterase. ACAT: a. To localize ACAT in the intestine (in the absence of cholesterol esterase) with respect to proximal and distal, villous tips and crypts and subcellular organelles. b. To determine the substrate specificity of ACAT in vitro, i.e., cholesterol specific or non-specific. c. To determine the physiological substrate(s) for ACAT, i.e., luminal and/or biosynthesized cholesterol. We also plan to describe the intestinal transport forms for luminal and biosynthesized cholesterol.